The invention relates to generally to a system and method for generating a spray or aerosol-type discharge, and relates more particularly to a system and method for generating a spray or aerosol discharge by means of a mechanical aerosol-tip mechanism which optimally controls the size of fluid particles in the discharge.
One of the problems encountered in the design of mechanical-spray or aerosol-type dispensers without a propellant gas is how to optimally control, and preferably reduce, the size of fluid particles to achieve an aerosol-type spray mist, and to narrow the range of the particle sizes, which translates into an optimal homogeneity of particle sizes. It is known in the art that mechanical energy losses incurred in the dispenser fluid conduit or channel, which energy losses are referred to as xe2x80x9chead losses,xe2x80x9d are a major contributing factor in the formation of larger fluid-particle sizes in the released aerosol spray. Such head losses may be caused by, for example, interaction of the moving fluid and stationary walls of the dispenser, changes in geometry of the conduit, and other significant changes in the fluid flow pattern.
Applying fundamental equations from classical fluid dynamics, it can be shown that the head losses are related to specific geometric parameters of the fluid conduit such as the length and inner diameter of the fluid conduit and the sharpness of turning angles in the fluid path. The Bernoulli equation expresses the head loss (HL) in terms of the energy conservation principle:                                           (                                                            p                  1                                γ                            +                                                V                  1                  2                                                  2                  ⁢                  g                                            +                              z                1                                      )                    -                      H            L                          =                  (                                                    p                2                            γ                        +                                          V                2                2                                            2                ⁢                g                                      +                          z              2                                )                                    (        1        )            
where p is pressure, V is velocity, xcex3 is fluid density, g is gravitational constant, and z is elevation head. The Darcy-Weisbach equation derives a formula for major head losses in terms of the physical parameters of the fluid channel assuming laminar flow.                                           H            L                    ⁡                      (                          M              ⁢                              xe2x80x83                            ⁢              a              ⁢                              xe2x80x83                            ⁢              j              ⁢                              xe2x80x83                            ⁢              o              ⁢                              xe2x80x83                            ⁢              r                        )                          =                              f            ⁡                          (                              L                d                            )                                ⁢                      (                                          V                2                                            2                ⁢                g                                      )                                              (        2        )            
where f is a friction factor, V is the fluid velocity, L is the conduit length and d is the conduit diameter. Furthermore, minor head losses can also be expressed in terms of physical parameters:                                           H            L                    ⁡                      (                          M              ⁢                              xe2x80x83                            ⁢              i              ⁢                              xe2x80x83                            ⁢              n              ⁢                              xe2x80x83                            ⁢              o              ⁢                              xe2x80x83                            ⁢              r                        )                          =                  K          ⁡                      (                                          V                2                                            2                ⁢                g                                      )                                              (        3        )            
where K is a minor loss coefficient related to specific geometry variations.
In addition to the physical parameters of the fluid and the conduit channel, another factor that affects the fluid-particle sizes in the released aerosol spray, for example in a one-way spray tip of the type described in U.S. Pat. No. 5,855,322, is the symmetry of the interface between the flexible nozzle portion, which distends in response to applied pressure, and the rigid shaft portion upon which the flexible portion normally rests. Asymmetries in the interface between the flexible portion and the rigid shaft, e.g., when the flexible portion is not properly centered on the rigid shaft, produce variable valve spacing, and result both in uneven fluid-particle size distributions, and in an overall increase of relatively large-sized fluid particles. FIG. 8 illustrates an example of asymmetry which may occur in aerosol tip mechanisms. FIG. 8 shows flexible left and right valve portions 401, 402 which are not symmetrically centered with respect to the rigid shaft 405. As can be discerned, the left flexible valve portion 401 overextends beyond the center axis of the rigid shaft 405, while the right flexible valve portion 402 under-extends. Other examples of asymmetrical interaction between the rigid shaft and the surrounding valve portions should be readily apparent.
A further problem in manufacturing spray/aerosol/dispensers is minimizing the number of components which constitute the spray/aerosol dispenser. As the number of components increases, the difficulty and cost of mass production consequently increases as well.
A further related problem is the costly development time needed for components from different subassemblies to be adjusted with the high precision required for alignment, e.g., in a sub-millimeter range.
It is an object of the present invention to provide a simple aerosol-type spray-tip mechanism (xe2x80x9caerosol tip mechanismxe2x80x9d), e.g., a spray-tip mechanism including a nozzle for dispensing liquid from a pump-type dispenser in aerosol or spray form, which nozzle maximizes the conservation of energy in the fluid flow by minimizing head losses.
It is yet another object of the present invention to provide an aerosol-tip spray-tip mechanism in which the components of the outlet valve are centered with respect to one another, e.g., with respect to the central elongated axis of the spray-tip mechanism, thereby ensuring a symmetrical outlet valve interface.
It is another object of the present invention to provide a method of ensuring the components of the outlet valve of an aerosol-type spray-tip mechanism to be centered with respect to one another, e.g., with respect to the central elongated axis of the spray-tip mechanism, thereby ensuring a symmetrical outlet valve interface.
In accordance with the above objects, the present invention provides an aerosol tip mechanism for an aerosol-type dispenser for dispensing liquid content by application of pressure, which aerosol-tip mechanism has a symmetrical outlet valve, i.e., the components of the outlet valve are centered with respect to the central elongated axis of the aerosol-tip mechanism. The aerosol tip mechanism according to the present invention may be adapted for use with a variety of types of liquid-dispensing apparatuses, for example, aerosol dispensers which channel liquid from a liquid reservoir through the aerosol tip mechanism by application of pressure via a pump mechanism.
In one embodiment of the aerosol tip mechanism according to the present invention, the aerosol tip mechanism has a flexible outer shell, a rigid cap portion composed of lower and upper portions, and a rigid nozzle portion having a rigid shaft received within the outlet portion of the flexible outer shell. The rigid shaft interfaces the outlet portion of the outer shell to form a first normally-closed valve. The lower and upper portions of the cap portion form boots which receives the outlet portion of the flexible outer shell and constrains lateral motion of the outlet portion of the outer shell. The boots of the cap symmetrically center the outlet portion of the flexible outer shell around the rigid shaft of the nozzle.
In the above-described embodiment, the aerosol tip mechanism further includes a swirling chamber that is laterally delimited by the rigid shaft of the nozzle in a central location and by the lower portion of the cap portion, and vertically delimited above by the outlet portion of the outer shell and underneath by the base connected to the rigid shaft. The aerosol dispenser is in fluid communication with a liquid reservoir from which liquid is channeled through a plurality of fluid channels within the rigid nozzle portion. Each of the fluid channels leads to one of a plurality of spiral feed channels that are gradually curved to minimize head losses as the liquid flows through the feed channels. Liquid channeled through the spiral feed channels continues in a spiral path into the swirling chamber in which the liquid is swirled before being released as an aerosol via the first normally-closed valve. The bottom of the trough (shown as 410 in FIG. 6 and FIG. 8) of the swirling chamber surrounding the nozzle central shaft, which trough receives the flow from each feed channel, has also been designed to minimize the head losses caused by collision of fluid arriving from fluid channels and fluid already orbiting in the trough. A ramp (shown as 411 in FIG. 6) at the end of each fluid channel raises the bottom of the trough so that when the liquid from a feed channel enters the trough, it is disposed at least partially under the already-orbiting fluid from the adjacent feed channel. This arrangement reduces fluid collisions, and as a consequence, when the liquid reaches the upper outlet of the swirl chamber, it has maximal celerity and pressure.
The aerosol tip mechanism of a fluid dispenser according to the present invention allows a smaller number of component parts to be assembled and also allows for improved concentricity of the component parts during production. During operation, the aerosol tip mechanism provides for lower head losses and more homogeneous particle sizes. When used in conjunction with a one-way outlet valve, the aerosol tip mechanism also provides for long-term sterility of the stored fluid, which in turn allows for preservation of the sterility of non-chemically preserved formulations. The fluid dispensed may be in form of suspension and liquid gels.